1. Field of the Invention
The present invention relates to a touch panel, and more particularly to a touch panel in which the silver lines occupy a smaller space, thus increasing the active area.
2. Description of the Prior Art
FIG. 1 is a front view showing the signal line structure of a conventional four-line touch panel. FIG. 2a is a cross-section taken along line A–A′ of FIG. 1. Referring to FIGS. 1 and 2a, the touch panel includes a top transparent substrate 100, a bottom transparent substrate 200, and an insulating spacer 600. An ITO (indium tin oxide) film 120 is coated on the lower surface of the top transparent substrate 100, and an ITO film 220 is coated on the upper surface of the bottom transparent substrate 200. The insulating spacer 600 is disposed between the ITO film 120 of the top transparent substrate 100 and the ITO film 220 of the bottom transparent substrate 200 to separate the two ITO films.
The so-called four-line touch panel indicates that the touch panel has a total of four signal sensing lines for sensing a signal. As shown in FIG. 1, top signal sensing lines 310 and 320 are disposed on two opposite edges of the top ITO film 120. Bottom signal sensing lines 410 and 420 are disposed on two opposite edges of the bottom ITO film 220. In addition, the touch panel further has four finer signal transmission lines, that is, a signal transmission line 310a connected to the signal sensing line 310, a signal transmission line 320a connected to the signal sensing line 320, a signal transmission line 410a connected to the signal sensing line 410, and a signal transmission line 420a connected to the signal sensing line 420. These four signal transmission lines transmit the sensed signals.
An adhesive (such as a double-sided adhesive 500) is disposed between the edges of the top and bottom ITO films 120 and 220, in order to separate the signal line from another ITO film or from another signal line. The area on the edges of the panel, in which signal lines are located, is referred to as a signal line area and is labeled “S”. The area outside the signal line area is an active area (AA).
When the top transparent substrate 100 is touched by an external force, such as a finger or stylus, electric contact occurs between the two ITO films 120 and 220, thus generating electric voltage. The signal is sensed by the signal sensing lines 310, 320, 410 and 420, and is then transmitted via signal transmission lines 310a, 320a, 410a, and 420a. 
As shown in FIG. 2a, symbol 320a is the signal transmission line on the top ITO film 120 and symbols 410 and 420 are the signal sensing lines on the bottom ITO film 220. To aid in understanding, the width ratio of the signal line area S in FIG. 2a is magnified in comparison with FIG. 1. It is to be understood from FIGS. 1 and 2a, that the silver line (signal line) arrangement of the conventional touch panel has the following disadvantages.
(1) The double-sided adhesive 500 is flat, but the silver line is of a protruding shape. Use of a flat double-sided adhesive to fasten the protruding silver line, reduces reliability.
(2) The thickness of the silver line is limited. In order to provide high conductivity, the width of the silver line is frequently increased, resulting in a larger overall appearance size.
(3) When the silver lines 320a and 420 between the two ITO films 120 and 220 are correspondingly aligned (as shown in FIG. 2b), the silver lines protrude, and short circuits easily occur between the two silver lines. Therefore, in order to maintain better insulation between silver lines, the top and bottom layer silver lines are disposed with an alternative alignment. For example, the silver lines 320a and 420 in FIG. 2a are disposed with an alternative alignment. Thus, the silver lines must occupy more space, causing a larger appearance size.